Diamond-type drill bit



Nov. 8, 1966 NORTH ET AL DIAMOND-TYPE DRILL BIT 2 Sheets-Sheet 1 Filed Aug. 17, 1964 CRITICAL WEAR AREA

F'IG.

m T N E V W.

DANIEL A.NORTH, JAMES C.POSG'ATE,JR. vf ATTORNEY Nov. 8, 1966 D. A. NORTH ETA!- 3,283,336;

DIAMOND-TYPE DRILL BIT Filed Aug. 1.7, 1964 2 Sheets-Sheet 2 SHAPE FACTOR (L/R) L50 2.00 2.50 3.00 1. .IO

. .oe SHAPE FACTOR, (L/R) vs. m e' (C) FOR DETERMINING Ko U) a; Z 2 O U 5 1| J. I! O v .03 .J 0

O X I L/R RATIO FIG. 4. INVENTORS.

DANIEL A. NORTH, BY JAMES C.FOSGATE,JR.

ATTORNEY.

United States Patent 3,283,836 DIAMOND-TYPE DRILL BIT Daniel A. North and James C. Posgate, Jr., Laredo, Tex., assignors, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed Aug. 17, 1964, Ser. No. 390,101 1 Claim. (Cl. 175-330) This invention relates to a drill bit of the type having diamonds or similar hard cutting elements afiixed thereto for the purpose of cutting or abrading away an earth formation. More particularly, the invention relates to an improved contour for diamond-type rotary drill bits.

Drill bits utilizing diamonds and similar hard materials as cutting elements enjoy peculiar advantages in drilling rock and other formations in connection with prospecting for oil wells and the like. When so utilized, the drill bits are detachably secured to the lower end of a drill pipe which is connected to a rotary drilling mechanism at the earths surface. Rotation of the drill pipe about its axis effects rotation of the drill bit to cut and abrade the earth material against which it is forced by the weight of the drill pipe above it, and more particularly by the weight of the heavy drill collars at the lower end of the drill string. Circulating fluid such as drilling mud is pumped down through the drill string and through the bit for the purpose of flushing away the cuttings and carrying the same to the upper end of the hole, to clean the cutting faces of the bit and the diamonds embedded therein, and to cool the cutting face and the diamonds.

Diamonds may be lost from the bit as the result of failure of the matrix in which the diamonds are embedded, or as the result of shattering of the diamonds during the course of drilling operations. Shattering of the diamonds may result from vibration inherent in a long drill string, vas a result of shock or impact as the bit skips or hops, or by improper dissipation of heat generated by the diamond while its abrading away the formation. The present invention is directed to a solution of the latter cause of diamond failure.

In accordance with the teachings of the present in vention, the contour of the cutting face of a diamond drill bit is such that the vertical force exerted on the drilling face during drilling operations decreases near the longitudinal axis of the drilling bit. The bit body is formed so as to have a central cutting portion and a gauge cutting portion, the central cutting portion extending inwardly and upwardly into the bit body from the lower end thereof to form a nonconverging throat, the throat terminating at a predetermined distance from the lower end of the bit so as to have a radius r thereat, the cross-sectional profile of the cutting portion being formed substantially according to the equation where erKoL is a constant having a value between .65 and 0.1, and preferably between .112 and .0205, x being measured along the longitudinal axis of the bit from the upper end toward the lower end of the central cutting portion, y being measured from the longitudinal axis of the bit, and L being the length of the throat from the upper end to the lower end of the central cutting portion.

Objects and features of the invention not apparent from the above discussion will become evident upon consideration of the following detailed description of the invention taken in connection with the accompanying drawing, wherein:

FIGS. 1 and 2 are cross-sectional views of prior art types of drilling bits herein shown for the purpose of illustrating the defects in the prior art;

FIG. 3 is a cross-sectional view of a drilling bit formed in accordance with the present invention; and

FIG. 4 is a rectangular coordinate graph useful in design calculations according to the invention.

With reference now to FIG. 1, there is shown a drilling bit having a stock 1 to which is aflixed a matrix 3 in which are embedded a plurality of diamond-type cutting elements 7. The lower end of the bit may be described as being semi-toroidal in cross section such that a cross section of the lower end of the cutting face of one-half of the bit is substantially semi-circular. The prior art bit illustrated in FIG. 2 having a stock 9, a matrix 11, and drilling elements 13 has a different drilling face cont-our such that the lower end 14 is shifted nearer the longitudinal axis of the bit. Each type of bit is usually provided with a multiplicity of water courses 5 for the purpose of allowing circulation of drilling fluid across the lower end of the bit. As the bits are rotated, a core is formed which may pass up through the center of the bit if the bit is used in coring type operations, or may be broken and passed through a side port if the bit is used in extended drilling operations. The means for disposing of the central core is not a part of this invention and is not described herein. Various types of means for disposing of cores are well known to the art. A particularly effective type is that illustrated and described in U.S. Patent 2,93 1,63 0, Grady.

The areas of the prior art type of drilling bits whereat failure of the diamond elements is most prevalent are indicated beneath the bits and designated by reference numerals 10 and 15. It will be noted that these critical wear areas are near the longitudinal axis of the bit. In these areas the heat dissipating capacity of the bit de creases whereas the cutting requirements remain quite high. The formation removed under any diamond is proportional to the cutting ability of the diamond, which is a function of the vertical component of the unit bearing load applied to that diamond, and of the linear tangential velocity, which latter quantity is a function dependent upon the distance of the diamond from the longitudinal axis of the bit. Manifestly, it is desirable to have the incidence of failure of the diamond equalized over the drilling face if the bit is to drill the greatest amount of hole during its drilling life.

With reference now to FIG. 3, there is shown a drill bit formed in accordance with the present invention.

The stock of the bit is designated by the reference numeral 17, the matrix by the reference numeral 19, and some of the diamond-type drilling elements by the reference numeral 21. The upper end of the stock of the bit is illustrated as having internal threads '23 as is customary when the bit is to be afiixed to a core barrel. However, a threaded pin may be utilized, such as illustrated in the Grady patent, supra. Furthermore, if the bit is to be used for the purpose of extended drilling operations rather than for the purpose of drilling a core, there must be incorporated core-breaking apparatus such as illustrated in the Grady patent, supra, or other types of core breakers known to the art. Such core-breaking apfined as the ratio of the throat length L to the working bit radius R. The factor K can be evaluated by a trial and error calculation where values of K which make the product K R equal to or less than 1.57 radians are subparatus is not illustrated inasmuch as it forms no part 5 stituted into the formula cos K R=e until it becomes of the present invention. It is assumed that drilling an equality. In FIG. 4 there is shown a graph of the fluid will circulate either down through the center of the quantity e =C as the function of the shape factor bit through flow channels and up the annulus between for use in evaluating K without resorting to trial and the drill pipe and the sides of the borehole, or in the reerror calculations. l verse direction, depending upon the drilling technique to The technique of determining the shape of the central be used. Fluid jet-forming ports also may be utilized cutting portion of a bit in accordance with the present such as are illustrated in the Grady patent, supra. invention will be best understood from the following It will be recognized that the profile of the drill bit is example. Let it be assumed that the bit outside diameter substantially the reverse of that utilized in diamond-type is 4% inches, that the pencil core size (i.e., 2 r is to be bits used heretofore, such as that illustrated in FIG. 2. 1 inch in diameter, and that the shape factor is to be The drilling face comprises a central cutting portion 27 2.00. Considering a A-inch fillet radius on the bit outextending from the lower end 29 of the bit inwardly and side diameter, the drilling diameter would be 4.25 inches. upwardly into the bit body and terminating at a distance The working radius is equal to one-half the drilling diam- L from the lower end 29 at a plane designated by the eter of the central cutting portion minus r which will reference numeral 31 whereat the drilling face has a give a value of 1.625 inches. Therefore, considering the radius r In effect, the drilling face forms a throat of shape factor of two, the throat length will be two times length L, of minimum radius r and of maximum radius the working radius, or 3.25 inches. The term KL can R, which later radius may be designated the working rabe f u fr m the formula dius of the drilling face. The drilling face also com- 1 prises a gauge cutting portion 33 extending upwardly and gutwardly from w lower end 29 of the which l to be equal to .9375 inf The formula for the profile e of any convenient form, for the purpose of cuttlng f t 1 n in be the hole to gauge. Diamond failure over the gauge cut- 0 6 can Ia cu mg For 10 W ting portion has not been found to be a problem, and Y: 1 -1 .0375(3.25) 1 warm-3.25)] the contour of the gauge cutting portion is not critical to -9375 the Present invention- Substituting various values of x between 0 and 3.25 in As indicated above, the cross-sectional cutting surface this formula will give the following table:

. X In. Ke mu- 0 m 0 Bad. 01 Rad. 11 g; 9152/Ko i z/ n+ =Y profile of the central cutting portion 27 of the bit is A coordinate plot of this table will yield the desired bit formed in accordance with the equation profile.

1 It is readily apparent that the bit profile resulting from y=r +(c0s o fl the present invention will produce a lower bearing pressure and will cause less abrading work to :be done per where diamond so that there is less heat to be dissipated by the To is the radius of the core diamond. However, this fact is compensated for 'by the e K0L is a constant having a value between .65 and 01, fact that there 18 a substantlal increase 1n the number of and usually has a value between .112 and .0205 55 i d as Progresses mlvardly toward h longitux is measured along the longitudinal axis of the bit from Simal axls i the cutting rate of the dnumg face the upper end toward the lower end of the central cut- 15 slibstalntlauy.equahzed m plane normal to the ting Portion 1%??? 11111113 1.? ail 3 221.31 32155.11; iiiifiiii ii y 15 measured from the longmldmal axls of the each area of the central cutting portion of the bit. There- The constant K, is determined from the equation fore, the probability of failure of the cutting elements is substantially equalized throughout the central cutting cos K R-e K.,R=1.57 radians the Although the embodiment dlsclosed 1n the preceding Manifestly, the working radius R ranges between the specification is preferred, other modifications will be aplimitation of 0 and'1.57 radians if K is set equal to unity, parent to those skilled in the art which do not depart while L may increase without limit. As L is increased, from the scope of the broadest aspects of the invention. the throat length of the bit becomes greater and the ratio What is claimed is: L/R becomes greater. In order to obtain a working A drill bit comprising a bit body having a central cutsolution, some parameter must be introduced whereby ting portion and a gauge cutting portion, said central cutthe working radius becomes the independent variable. ting portion extending inwardly and upwardly into said The diameter of the hole to be drilled, and therefore the bit body from the lower end thereof to form a non-conradius of the bit, will always be known. The parameter verging throat, and terminating therein at a predeterrelating the working radius R and the throat length L to mined distance from said lower end, said throat having a K may be termed the shape factor, which can be deradius r at said predetermined distance from said lower end, the cross-sectional profile of said central cutting portion :being formed substantially according to the equation Where r is the radius of the core e is a constant having a value between .65 and .01

x is measured along the longitudinal axis of the bit from 10 the upper end toward the lower end of the central cutting portion y is measured from the longitudinal axis of the bit.

References Cited by the Examiner UNITED STATES PATENTS 10/1929 Nisho 175404 9/1952 Catallo 175-330 10/1952 Zublin 175329 8/1961 Pennington 175--329 FOREIGN PATENTS 12/1962 France.

CHARLES E. OCONNELL, Primary Examiner.

N. C. BYERS, Assistant Examiner. 

